In the past, soil additives and plant fertilizers have been made synthetically from petroleum by-products and mineral salts. However, increasing public awareness of the environmental drawbacks of using chemical-based fertilizers has created a demand for safe, natural and more environmentally friendly fertilizers.
Waste organic materials such as waste from the food industry can be used to produce plant and soil fertilizers. Such fertilizers are relatively cheap to produce, and are also environmentally friendly, as they are made from a renewable resource, rather than non-renewable petroleum products. Another important advantage of such fertilizers over petroleum-based fertilizers is that they can improve the health of the soil, which in turn improves the health and yield of the plants. Organic fertilizers contain micronutrients and macronutrients that are not found in chemical fertilizers. The most important macronutrients are nitrogen, phosphorus and potassium. Secondary macronutrients include calcium, magnesium and sulfur. Micronutrients are elements essential for plant growth that are required in trace quantities. Important micronutrients include boron, copper, iron, chloride, manganese, molybdenum and zinc. In addition to these essential elements, “organic” fertilizers (e.g. not petroleum-based or otherwise chemical fertilizers) contain amino acids that aid plant and soil health. Organic fertilizers replenish the nutrient level of the soil and feed important soil organisms, such as nematodes, earthworms and microorganisms, which are essential for overall plant and soil health.
Chemical fertilizers do not contain the micronutrients and macronutrients found in organic fertilizers. As such, chemical fertilizers can only treat plants but not the soil. Also, chemical fertilizers may kill important soil organisms and tend to be readily leached from the soil, as they are usually composed of water soluble inorganic compounds that are easily washed away. Thus, chemical fertilizers are not retained long enough to have a significant effect on plant growth, while the chemicals leached from the soil can cause environmental damage, by pollution of nearby bodies of water.
A type of organic fertilizer is fertilizer produced from fish or fish by-products, which utilizes whole fish or fish parts left over from food processing. The use of the term “fish” throughout the application will be used to refer to whole fish, fish parts or by products of fish processing, unless stated otherwise. Fish fertilizer can be produced in two ways: (a) the formation of a fish emulsion; and (b) the hydrolysis of whole fish or fish parts to produce hydrolyzed fish fertilizer.
To produce a fish emulsion, whole fish or fish by-products are heated to extract oils and the solid material is pressed into a cake and dried to make fish meal, which can then be used for livestock feed. The liquid residue that has been pressed out of the fish cake is the fish emulsion used for fertilizer. There are two main drawbacks associated with fish emulsion fertilizer. Fish emulsion has a very strong, unpleasant odour due to the presence of decomposing proteins, caused by the high temperatures used during the fish extraction process. As fish emulsion is composed of the liquid pressed out of the fish cake, fish emulsion is primarily composed of water soluble nutrients and contains a relatively low concentration of oil-soluble nutrients. Therefore, fish emulsion is lacking in a number of macro and micro nutrients including oils, proteins and vitamins that are beneficial for optimal plant and soil health.
The second method of preparing fertilizer from fish involves the hydrolysis of whole fish or fish parts to produce hydrolyzed fish fertilizer. In this method, the starting material is ground into meal and then digested or hydrolyzed. There are numerous methods of hydrolyzing fish protein to break down solid fish into a liquid form, which fall into two categories: (1) enzymatic hydrolysis and (2) chemical digestion.
Fertilizer produced by the fish hydrolysis process has a number of advantages over fertilizer produced by the fish emulsion process. The hydrolysis process retains much more of the nutrients than the emulsion process, as the hydrolysate utilizes all of the starting material. In particular, hydrolyzed fish fertilizer retains the oil soluble nutrients which are excluded from fish emulsion. Therefore, hydrolyzed fish fertilizer provides superior results to fish emulsion fertilizer, as it contains the full spectrum of nutrients. Hydrolyzed fish fertilizer contains essential oils, vitamins, trace minerals, enzymes, and amino acids, which feed important soil organisms and are taken up more easily by the plant roots. Another advantage of the hydrolysis process is that it usually does not involve high temperatures. Consequently, the hydrolysate has very low odour as it does not contain decomposing proteins.
In some instances, consumers may wish to continue using chemical fertilizers as they are cheap and easy to apply. Organic fertilizer, including fertilizer prepared from fish, can also be used as an additive to regular chemical fertilizer. By using organic fertilizer as an additive, the chemical fertilizer is supplemented with nutrients found in organic fertilizer but not in chemical fertilizer.
In enzymatic hydrolysis, either preparations of enzymes or microorganisms are used to hydrolyze proteins into smaller peptides. The digested fish meal is then filtered to produce a whole fish hydrolysate composition. An example of enzyme hydrolysis is found in U.S. Pat. No. 5,393,318.
Enzymatic hydrolysis of fish can be carried out using preparations of enzymes such as papain, which break down proteins into smaller peptides and individual amino acids. However, enzymes are sensitive to pH and temperature, as well as the presence of inhibitors and denaturants. Enzymes will only catalyze reactions within a specific pH and temperature range. Therefore, the hydrolysis reaction must be carefully monitored and controlled. As enzymes must be isolated and refined from natural sources without destroying their catalytic activity, this further increases the manufacturing cost. Enzymatic hydrolysis of fish can also be carried out with microorganisms, e.g. anaerobic digestion as disclosed in U.S. Pat. No. 4,022,665 and U.S. Pat. No. 4,975,106.
Hydrolysis of fish protein can also be effected with chemicals. However, due to the strength of the peptide bond, stringent conditions, i.e. concentrated acid or base and heat are usually required to completely hydrolyze the fish protein. In U.S. Pat. No. 4,043,788, fish is hydrolyzed with potassium hydroxide and heating, and then neutralized with phosphoric acid. In U.S. Pat. No. 4,383,845, fish solids are digested with ammonia under 300 psi with steam. Chinese Patent 1207380 uses formic acid, sulfuric acid and propionic acid at 80-90° C. Japanese Patent No. 4037679 describes refluxing defatted fish skin in 4 to 8 N phosphoric acid. However, as noted above, the application of heat causes the decomposition of fish protein, which produces unpleasant odours. Moreover, the application of heat to fish protein generally results in a reduction in the concentration of micronutrients such as molybdenum.
A common drawback of hydrolyzed fish fertilizers is inefficient hydrolysis or uneven mechanical breakdown of the fish protein during processing, which creates a mixture of liquid and solid fish particles. This creates a fertilizer product of high viscosity that is difficult to handle, such as measuring and mixing to desirable strengths for spraying from commonly available agricultural equipment.
Accordingly, there is a need for alternative processes that overcome the above-noted drawbacks.